DUBLIN (Reuters) - Northern Ireland’s largest Irish nationalist party Sinn Fein stepped up calls on Wednesday for a split from the United Kingdom, saying a referendum on Irish unity should be held in the event of a ‘no deal’ Brexit.

Sinn Fein has been regularly calling for a vote for Northern Ireland to leave the UK and unite with the Republic of Ireland since Britain voted to leave the European Union in 2016 while most voters in Northern Ireland voted to remain.

However its leader, Mary Lou McDonald, raised the demand for the second successive day in the Dublin parliament, where - separate to their colleagues in the devolved assembly in Belfast - its lawmakers make up the third largest party.

“A crash out Brexit will be catastrophic for our island. It will rupture our economy, our social fabric and our peace accords so the contingency planning required goes well beyond the recruitment of additional officials,” McDonald told Irish Prime Minister Leo Varadkar.

“In the event of a no deal situation arriving, it is the strong view of Sinn Fein that a referendum on unity must be advanced as a matter of urgency and priority.”

Varadkar dismissed the timing of Sinn Fein’s call as “destructive and disruptive”, a day after McDonald said she raised it in a telephone call with British Prime Minister Theresa May, whom she said also disagreed with her.

“I don’t believe now is the time for us to start talking about border polls,” Varadkar said.

Under a 1998 peace deal that ended 30 years of sectarian violence in the province, the British government can call a referendum if it appears likely a majority of those voting would seek to form part of a united Ireland.

A LucidTalk/Times newspaper poll on Friday showed that if there was a referendum next year, 30 percent of voters would definitely vote for a united Ireland if Britain leaves the EU on the terms Theresa May is currently proposing, but that would rise to 48 percent if Britain quit the bloc without a deal.

The pollsters said the opposition to holding a referendum was driven by pro-British unionists who want Northern Ireland to remain part of the UK with the province’s Irish nationalists leading calls for a vote.

When deferring a parliamentary vote on her deal this week, May told lawmakers that if they cared about preserving the union between England, Scotland, Wales and Northern Ireland, they should listen to the people of Northern Ireland who she said supported her deal.